The primary role of sodium in ion transport and the central importance of calcium in membrane processes make the interaction of these ions in transport mechanisms worthy of study. In this project, an attempt will be made to analyze transepithelial fluxes of sodium and later calcium ions under the influence of gradient of electrical and chemical potential, and in the presence and absence of solvent drag. An equation suitable to the analysis of homogeneous array of parallel with linear conductance has been developed and tested under certain experimental conditions in toad bladder. Further study of the applicability of this formulation to sodium transport in toad bladder and other epithelia will be carried out followed by a study of its applicability to calcium transport, and finally to the interaction between these processes as exemplified by agents and drugs which have well recognized effects upon transport of these two cations.